A plasma process is often performed under a vacuum atmosphere by vacuuming gas from a processing chamber. In such case, a workpiece is placed on an electrostatic chuck (ESC) that is arranged on a mounting table within the processing chamber.
The electrostatic chuck includes a chuck electrode made of a conductive sheet and dielectric members arranged on a surface and a backside surface of the chuck electrode. A workpiece such as a wafer is electrostatically attracted to the electrostatic chuck by a Coulomb force that is generated when a voltage from a DC voltage supply is applied to the electrostatic chuck. A plasma process is performed while the workpiece is electrostatically attracted to the surface of the electrostatic chuck as described above. In some cases, a heat transfer gas may be supplied between a backside surface of the wafer and the surface of the electrostatic chuck.
When the plasma process is completed, voltage application to the electrostatic chuck is stopped so that a Coulomb force may not be generated, and the workpiece is de-chucked from the electrostatic chuck. An exemplary method of de-chucking the workpiece may involve raising support pins that are embedded within the mounting table and lifting the workpiece from the electrostatic chuck.
In order to de-chuck the workpiece in a more reliable manner, a discharge process is performed for discharging (removing) an electric charge remaining in the electrostatic chuck and the workpiece. For example, after stopping the voltage application to the chuck electrode, an inert gas may be introduced into the chamber and the pressure within the chamber may be maintained at a predetermined pressure. Further, a high frequency power for plasma generation may be applied to generate a plasma that is weak enough to be incapable of etching the workpiece, and a discharge process may be performed by moving the residual charge residing within the electrostatic chuck and the workpiece into a plasma space.
For example, in Patent Document 1, after a plasma process is completed, a high frequency power that is weak enough to be incapable of etching a wafer is applied and the supply of a heat transfer gas is stopped. The ions or electrons within a plasma generated by the high frequency power enter between a surface of the wafer and a surface of the electrostatic chuck to neutralize a residual charge charging the surface of the wafer from a peripheral edge portion of the wafer toward the center of the wafer. Pins are raised as the above neutralization progresses, and the wafer is thereby de-chucked.